1. Field of the Invention
The present invention relates to an apparatus and a method for effectively recovering acetic acid and catalyst from a mother liquor discharged from a series of processes including an oxidation process, a crystallization process and a solid-liquid separation process, in a continuous process for preparing naphthalenedicarboxylic acid by oxidizing dimethylnaphthalene in the presence of an oxygen-containing gas and an acetic acid solvent, using a catalyst system comprising a transition metal such as cobalt or manganese, and a bromine-based compound.
2. Description of the Related Art
In general, a variety of separation processes can be employed to recover acetic acid and catalyst that have been used in the process.
For the method of recovering acetic acid, it is common to use an acetic acid recovery process using a distillation method, but this process is economically unfavorable. Meanwhile, a filtration method and an absorption method are not suitable for separating acetic acid and catalyst. Thus, a variety of different methods for recovering acetic acid and catalyst have been suggested. U.S. Pat. No. 4,883,912 describes a process for recovering acetic acid by extracting acetic acid from an acetic acid solution containing metallic substances, using tertiary amine and an organic diluent as the solvent for acetic acid extraction. However, this method is not suitable as the method for recovering acetic acid and catalyst in the process for preparation of naphthalenedicarboxylic acid, because the method of extraction requires a post-treatment process after the separation and recovery of acetic acid, and the reactivities of the solvent for extraction and of the oxidation catalyst need to be taken into account.
There are available an incineration method, a vacuum filtration method, and an electrochemical method as the methods for catalyst recovery, but these methods are still not commercialized.